The family Bacillaceae (domain Bacteria; kingdom Bacteria; phylum Firmicutes; class Bacilli; order Bacillales) (Fig. 1) is a globally dispersed and phenotypically heterogeneous group of bacteria (1, 2). It therefore follows that the family possesses a considerable evolutionary history for scientists to unravel. In recent years, the issue of evolution in the Bacillaceae has been probed from two directions. Some researchers have taken an ecological approach to understand the organisms’ adaptive evolution to particular environmental niches; others have pursued a laboratory-based approach in which single laboratory strains are directed to evolve under particular conditions determined by the experimenter. Both approaches have yielded new insights. As in so many other facets of the biology of the Bacillaceae, most of our knowledge has been derived from the intense study of relatively few members of the family, most notably Bacillus subtilis (3, 4). Much less information has been obtained concerning the vast majority of the Bacillaceae, prompting the present examination of diversity and evolution within this ubiquitous family. The present article builds upon previous reviews of the topic (5–10). Additional information on the genomic diversity of spore-forming Firmicutes and on the ecology of the Bacillaceae can be found in articles by Galperin (480) and Mandic-Mulec et al. (481).

Plots of D value versus temperature for B. subtilis 168 spores suspended in water (open circles) or in saturated NaCl (filled circles). The lines are best-fit extrapolations of the data to ambient temperature (25°C; thick vertical line). Data are averages of triplicate determinations that varied by less than 5%.

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10.1128/9781555819323/fig2-2.gif

Figure 2

Plots of D value versus temperature for B. subtilis 168 spores suspended in water (open circles) or in saturated NaCl (filled circles). The lines are best-fit extrapolations of the data to ambient temperature (25°C; thick vertical line). Data are averages of triplicate determinations that varied by less than 5%.

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